I haven't been on the Explorer yet (7/14/06) but I have been on the Majesty, Splendour, Grandeur (2X), Radiance, Vision and Voyager and they all had salt water pools. I don't think any have fresh water, although it would be nice.

I also have not been on Explorer but all other RCCL ships seem to have salt water. In fact I think, with the exception of Princess who does use fresh water, all the big cruise lines fill their pools with salt water.